Photoelectric polarization analyzer

ABSTRACT

Photoelectric polarization analyzer of this invention includes polarization system consisting of a linear polarizer or a polarizing orientation oscillating K.D.P. elements, quarter-wave plate and a compensator; an analyzer; another quarter-wave plate provided between the analyzer and a specimen; an electric device for separating two photoelectric signals converted by a photoelectric element from the light transmitted through said other quarter-wave plate into two electric control signals. In the prior art one of the control signals is used to rotate the polarization system for compensating the orientation of the specimen, and the other control signal is used for shifting the compensator for compensating the phase difference. However, in this invention a half-wave plate is interposed between the polarization system and is and the specimen rotatable in a plane perpendicular to the optic axis of the polarization system, and said one of the two signals is applied to the half-wave plate to rotate it instead of rotating the polarization system, which simplifies the structure.

United States Patent Yamamoto et al.

[ Aug. 29, 1972 [54] PHOTOELECTRIC POLARIZATION Primary ExaminerWilliamL. Sikes ANALYZER Attorney-Ward, McElhannon, Brooks & Fitzpatrick [72]Inventors: Tadaaki Yamamoto; Toshiyuki Kasai, both of Kawasaki, Japan[57] ABSTRACT Photoelectric polarization analyzer of this invention [73]Asslgnee' Nlppon Kogaku includes polarization system consisting of alinear [22] Filed: Dec. 23, 1970 polarizer or a polarizing orientationoscillating I(.D.P. elements, quarter-wave plate and a compensator; an[21] Appl l0l070 analyzer; another quarter-wave plate provided betweenthe analyzer and a specimen; an electric [30] Foreign ApplicationPriority Data device for separating two photoelectric signals convertedby a photoelectric element from the light trans- Dec. 29, 1969 Japan..44/ 123910 mined through Said other quartepwave plate into twoelectric control signals. In the prior art one of the con- (gl "356/124601 signals is used to rotate the polarization System for compensatingthe orientation of the Specimen and the [58] Field of Search ..356/114,115, other Control Sign a1 is used for Shifting the compensa tor forcompensating the phase difference. However, in this invention ahalf-wave plate is interposed [56] References Cted between thepolarization system and is and the TED STATES ATE specimen rotatable ina plane perpendicular to the optic axis of the polarization system, andsaid one of 2,409,853 10/1946 Henn .356 14 the two signals i applied tothe ha1f wave plate to et a1 t t i t d f t ti g th p l i ti y t3,520,615 7/1970 Smith ..356/l14 which Simplifies the structure3,545,867 12/1970 Rostas ..250/225 2 Claims, 9 Drawing Figures RELATIONOF s n s s ORIENTATION 9 9 9 l l i i l i i L amona cilia 2 3 5T HH 1 L 52. 25 e5 6 6 J l2 Dv k I? I 03 SERVO SERVO MOTOR MOTOR 9 8 4 l S l SERVOERvo AMP. AMP.

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PAIENIEmum I912 3,687,555 sum 3 nr-3 PHOTOELECTRIC POLARIZATION ANALYZERFIELD OF THE INVENTION This invention relates to a photoelectricpolarization analyzer and more particularly to a polarization analyzercapable of measuring two polarization variables of a specimen placed inan arbitrary orientation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view forexplaining the prior art photoelectric polarization analyzer;

FIG. 2 is a diagrammatic view showing a preferred embodiment inaccordance with the present invention;

FIG. 3 is a circuit diagram of an oscillator used in the instrumentsshown in FIGS. 1 and 2; and

FIGS. 4(a) 4(f) illustrate Poincare sphere for explanation of thepresent invention.

DESCRIPTION OF THE PRIOR ART The prior art polarization analyzer shownin FIG. 1 has a polarization system D comprising at least a linearpolarizer P, crystals X and X such as potassium dihydrogen phosphate(K.D.P.) whose birefringence varies upon application of a voltage, aquarter-wave plate Q and a compensator C. The two variables whichdetermine the state of polarization are simultaneously modulatedv andthe polarized light beam is made incident upon a photoelectric tube 3through a specimen S oriented in an arbitrary direction, a quarter-waveplate Q and an analyzer A. Two photoelectrical signals generated in thephotoelectric tube 3 may be separated by their phase difierence (of 90).The polarization system D is rotated about its optical axis by one ofthe separated signals so that the orientation of the specimen may becompensated for while the corn pensator C in the system D is shifted inresponse to the other separated signal to thereby compensate for thephase difference of the specimen. Thus, the two variables (orientationand phase difierence) of the specimen may be measured by the angle ofrotation of the polarization system D and shift of its compensator C.The component parts designated by reference nu merals 4 12 are alsoemployed in an instrument shown in FIG. 2, which shows a preferredembodiment of the present invention.

In the prior art photoelectric polarization analyzer of the typediscussed above, the polarization system D must be rotated in order tocompensate for the orientation of the specimen so that the constructioninevitably becomes bulky and complex. Therefore, the instrument becomeslarge in size.

SUMMARY OF THE INVENTION The primary object of the present invention isto provide a photoelectric polarization analyzer which can eliminate thedisadvantages described above.

According to the invention, between the conventional polarizing opticalsystem and the specimen, a half-wave plate is provided which isrotatable in a plane perpendicular to the optical axis of saidpolarizing optical system so that the structure becomes very simple.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention willbecome more apparent from the following description of one preferredembodiment thereof taken in conjunction with the accompanying drawing.Referring to FIG. 2, reference character L designates a light source; 1,an illumination system; P, a linear polarizer whose orientation is 0 asa reference orientation for other components; X a K.D.P. element whoseprincipal axis is 45 and to which is applied the AC voltage (rectangularwave) EX as shown in FIG. 3 from an oscillator 12; O is a quaterwaveplate whose principal axis is 0. As shown in FIG. 4 (a) the lightrepresented by the point P on the Poincare sphere is modulated so as tooscillate along the equator. Another I(.D.P. element X has its principalaxis oriented at 45 and to which is applied the AC voltage (square wave)EX out of phase with the AC voltage EX so that the light represented bythe point P in FIG. 4 (b) may be modulated with respect to the phasedifference to thereby make a very small oscillation along a great circlePNA. Thus, as shown in FIG. 4 (c), the light P is simultaneouslysubjected to the above two modulations.

A Soleil-Babinet compensator C, whose principal axis is oriented at 45,is mechanically coupled to a servomotor 11 in order to compensate forthe phase difference. The polarization system D comprises a linearpolarizer P, a K.D.P. element X a quarter-wave plate 0,, another K.D.P.element X and the compensator C. A half-wave plate H is mechanicallycoupled to a servomotor 10 in order to rotate it about the optic axis soas to compensate for the angle of orientation. A specimen S may beplaced in any orientation. A quarter-wave plate Q has its principal axisoriented at 45. An analyzer A is oriented at 90. Reference numeral 2designates an optical system for observation; 3, a photoelectric tube;and 4, an amplifier for amplifying the photocurrent generated by thephotoelectric tube 3. The components of the signals from the amplifier4, which are in phase with the signals from the oscillator 12, arerectified by synchronous rectifiers 5 and 6. The V DC current from thesynchronous rectifier 6 is converted into 50 cps AC by a converter 7.Reference numerals 8 and 9 designate servoamplifiers; and 10, the ACservomotor of 50 cps for rotating the half-wave plate H for compensatingfor the orientation. The servomotor 11 is a DC servomotor coupled to theSoleil- Babinet compensator C for compensating for the phase difference.The oscillator 12 together with components 13-15 as shown in FIG. 3apply, to the K.D.P. elements X and X the AC voltages (square waves) EXand EX which are out of phase by 90. That is, reference numeral 13designates a pulse generator 14, 14' and 14", capacitors; and 15, 15 and15", bistable multivibrators. The bistable multivibrator 15 is actuatedby the signals from the pulse generator 13 through the capacitor 14 sothat two outputs, which are out of phase by are derived. These twooutputs or signals are used to actuate the bistable multivibrators 15'and 15" through the capacitors 14' and 14'', respectively, so that twosignals, out of phase by 90, are derived. The device, including thecomponents 4 12, will be referred to hereinafter as an electricseparating device.

Next will be described the mode of operation for automaticallycompensating for the orientation and phase difference of the ellipticalpolarization when the specimen is orientated at some arbitrary angle.The intensity of light passing through the optical system shown in FIG.2 is given by the following equation:

The fundamental modulated frequency component of the transmitted lightis given by the following equation:

1 d+K cos (mass-l) 2.1.01 sin 'wt +K2 sin (2-2B- 2J1(A) cos wt whereangle of rotation of the M2 plate H;

o'= phase difference of the specimen;

01: phase dilference of the Soleil-Babinet compensator C;

J A Bessel functions of the first order; and

K K constants. (See FIG. 4 (1')) That is, the photoelectric signalcontains the signal components of sin wt and cos wt. The signalcomponent of sin Wt is vanished when 0' c 7T4 0', while the signalcomponent of cos wt is to vanish when 20 2 1r/2.

The signal component of sin wt is vanished by the phase-differencecompensation by the Soleil-Babinet compensator C, while the signalcomponent of cos wt is vanished by adjusting the angle of rotation 0 ofthe M2 plate H. Therefore the signal with the phase of sin wt is appliedto the synchronous rectifier 5 by the oscillator 12 so that therectifier 5 may rectify only the signal component of sin wt out of thephotocurrent. Thus the servomotor 11 may compensate for the phasedifference by the signal component of sin wt. In a similar manner theoscillator 12 gives the signal with the phase of cos wt, to thesynchronous rectifier 6 so that the servomotor 10 may adjust theorientation only by the signal component of cos wt.

The mode of operation will be further described with reference to thePoincare sphere. By following the path of the light, completely vanishedby the analyzer A, the polarization of the light, before passing throughthe specimen S with the phase difference a, is given at E. Theservomotor 10 rotates the half-wave plate H through a half of an anglebetween the points P and P at which the great circle EN containing thepoint E and the pole N, intersects the equator (up to thereby adjustingthe orientation. For phase difference compensation, the servomotor 11rotates the compensator C through oc. Thus, because of the half-waveplate H, the point E is given. The orientation adjustment as well as thephase difference compensation are accomplished simultaneously.

.With the structure mentioned above, by orientating the specimen 8 atsome arbitrary angle, and applying A.C. rectangular voltages EX and EXout of phase by 90, from the oscillator 12 to K.D.P. elements X and Xrespectively, the orientation angle modulation and phase differencemodulation are given to the light passing through the linear polarizerP.

The intensity of the transmitted light is converted into photocurrentincluding two signal components, which are separated and amplified fordriving the servomotorslil and 11. Therefore, the half-wave plate H andthe compensator C are rotated to thereby adjust the orientation andcompensate for the phase difference, respectively. Thus, the twovariables of the polarization may be measured from the adjustment andcompensation.

It is seen that, instead of the elements X and X a substance whichbrings about the Faraday Efiect when subjected to a strong magneticfield may be employed. When l(.D.P elements, which can withstand ahalfwave voltage are employed, the following variant becomes possible.In addition, instead of the Soleil- Babinet compensator, the K.D.P.element X may be employed. The double-refraction phase difference of theK.D.P. element is linearly proportional to the voltage applied so thatin addition to the AC voltage, the DC voltage is applied across theK.D.P. element X so as to vary the applied voltage to thereby accomplishthe phase difference compensation, as is the case of the Soleil-Babinetcompensator. In this case, the degree of the phase differencecompensation may be measured from the voltage applied. In this methodthe mechanical error in the phase difference compensation may beeliminated and the construction of the instrument may be made compact insize, because no compensator is employed.

We claim:

1. Photoelectric polarization analyzer for automatically measuring twopolarization variables (orientation and phase difference) comprising incombination:

an illuminating optical system (L);

a linear polarizer (P) disposed serially along the optical axis of saidilluminating system;

means (X Q for modulating the orientation of the light passing throughsaid linear polarizer;

means (X for modulating a phase diflerence of the light passing throughsaid linear polarizer;

a phase difference compensator (C) disposed slidably in the normaldirection to the optical axis of said illuminating system, theorientation of the principal axis of said phase difference compensator(C) being at 45 with respect to the optical axis of said polarizer;

a half-wave plate (H) disposed rotatably in said optical path and behindsaid phase difference compensator;

a specimen (S) disposed behind the half-wave plate at arbitralorientation;

a first quater-wave plate (0;) disposed behind the specimen, theorientation of the principal axis of the first quater-wave plate beingat 45 with respect to said linear polarizer;

an analyzer (A) disposed behind the quater-wave plate, the principalaxis of the analyzer being at with respect to the principal axis of saidlinear polarizer;

photoelectric conversion means for converting a photo-signal includingtwo components modulated by said orientation and phase differencemodulation means, respectively, into an electric signal ineluding twoelectric modulation signal components; and

an electric control means for dividing said electric signal into saidtwo modulated components, one component thereof being modulated by therotation of said half-wave plate (H) to compensate for the orientationof the specimen, and the other component being modulated by sliding saidphase difierence compensator (C), to compensate for the phase differenceof the specimen,

whereby the orientation and the phase difference of the specimen isautomatically measured as the angle of rotation of said half-wave plateand the length of movement of said phase difference compensator.

2. Photoelectric polarization analyzer according to claim 1, whereinsaid orientation modulation means comprises a first double refractionelement (X disposed behind said linear polan'zer (P) and having anelectro-opfical effect, the orientation of the principal axis of thefirst double refraction element being at 45 with respect to theprincipal axis of said linear polarizer,

a second quater-wave plate (Q disposed between said first doublerefraction element and said phase difference modulation means, theorientation of the principal axis of the second quater-wave plate beingat 0 or with respect to the principal axis of said linear polarizer;

an oscillator for applying an electric voltage to said first doublerefraction element; and

said phase difference modulation means comprises a second doublerefraction element (X disposed between said second quater-wave plate andsaid phase difierence compensator (C) and having an electro-opu'caleffect, the orientation of the principal axis of the second refractionelement (X being at 45 with respect to said linear polarizer, and

an oscillator for applying to the second double refraction element (X anelectric voltage whose phase differs by 90 from that of said voltageapplied to said first double refraction element (X P UNITED STKTESPATENT OFFICE (s/ss) CERTIFICATE OF CORRECTION Patent: No. 7, 555 DatedAdgust 29, 1972 TADAAKI YAMAMOTO arid TOSHIYUKI KASAI Inventoi-(s) It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

- In the Abstract, lines 16 and 17, which read "between the polarizationsystem and is and the specimen" should read between the polarizationsystem and the "specimen and is Signed and sealed this 6th day of March1973.

(SEAL) Attest:

EDWARD M.FLE TCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. Photoelectric polarization analyzer for automatically measuring twopolarization variables (orientation and phase difference) comprising incombination: an illuminating optical system (L); a linear polarizer (P)disposed serially along the optical axis of said illuminating system;means (X1, Q1) for modulating the orientation of the light passingthrough said linear polarizer; means (X2) for modulating a phasedifference of the light passing through said linear polarizer; a phasedifference compensator (C) disposed slidably in the normal direction tothe optical axis of said illuminating system, the orientation of theprincipal axis of said phase difference compensator (C) being at 45*with respect to the optical axis of said polarizer; a half-wave plate(H) disposed rotatably in said optical path and behind said phasedifference compensator; a specimen (S) disposed behind the half-waveplate at arbitral orientation; a first quater-wave plate (Q2) disposedbehind the specimen, the orientation of the principal axis of the firstquater-wave plate being at - 45* with respect to said linear polarizer;an analyzer (A) disposed behind the quater-wave plate, the principalaxis of the analyzer being at 90* with respect to the principal axis ofsaid linear polarizer; photoelectric conversion means for converting aphoto-signal including two components modulated by said orientation andphase difference modulation means, respectively, into an electric signalincluding two electric modulation signal components; and an electriccontrol means for dividing said electric signal into said two modulatedcomponents, one component thereof being modulated by the rotation ofsaid half-wave plate (H) to compensate for the orientation of thespecimen, and the other component being modulated by sliding said phasedifference compensator (C), to compensate for the phase difference ofthe specimen, whereby the orientation and the phase difference of thespecimen is automatically measured as the angle of rotation of saidhalf-wave plate and the length of movement of said phase differencecompensator.
 2. Photoelectric polarization analyzer according to claim1, wherein said orientation modulation means comprises a first doublerefraction element (X1) disposed behind said linear polarizer (P) andhaving an electro-optical effect, the orientation of the principal axisof the first double refraction element being at 45* with respect to theprincipal axis of said linear polarizer, a second quater-wave plate (Q1)disposed between said first double refraction element and said phasedifference modulation means, the orientation of the principal axis ofthe second quater-wave plate being at 0* or 90* with respect to theprincipal axis of said linear polarizer; an oscillator for applying anelectric voltage to said first double refraction element; and said phasedifference modulation means comprises a second double refraction element(X2) disposed between said second quater-wave plate and said phasedifference compensator (C) and having an electro-optical effect, theorientation of the principal axis of the second refraction element (X2)being at 45* with respect to said linear polarizer, and an oscillatorfor applying to the second double refraction element (X2) an electricvoltage whose phase differs by 90* from that of said voltage applied tosaid first double refraction element (X1).